Vapor phase extraction



. Parental nee. 18,1945

I AUNITED STATE varon rnasn Ex'rnAcrroN Chester L. Bead, Westeid, N. J., assigner to Standard Oil Development Company, a corporation of Delaware Application august 27, 1942. serial No. 45ans t v clama (ci. eso-cw The present invention relates improvements in the artv of extracting desirable hydrocarbons from 'a mixture thereof, and, more particularly,

it relates to the fractionation of a relatively wide boiling range hydrocarbon fraction by vapor phase extraction to separate the individual types oi componentsand to obtain high yields of each component in a relatively pure state.

Heretoiore, in the ordinary vapor phase extraction of wide boiling range fractions, it has beenl possible to obtain one of the components in a fairly pure state with limited yield or to obtain a fairly high yield of this component with limited purity, but it was not possible to obtain both a high yield and high purity by vapor phase extraction alone. For example, in the recovery of toluene iroma hydrocarbon fraction which had been subjected toreforming in the presence of hydrogen and a catalyst, it was not possible to obtain toluene by vapor phase 'extraction in a viorm sufdciently pure for use in nltration.

In order to concentrate substantially all ,of the toluene contained in a Wide boiling stock by distillation in commercially available equipment, it

ene in a fairly pure state but an extremely complicated separating procedure would be necessary.

According to my present invention, I secure high yields oi the desired component, such as toluene, in a high state of purity by a process which involves in brief compass distilling a wide boiling range feed stock and recovering therefrom a fraction containing substantially all of the desired hydrocarbon, such as toluene. This fraction is thensubjected to vapor phase extraction to obtain the maximum yield of non-aromatic hydrocarbons overhead. The extract phase,

'which may be admixed with an added anti-solvent. is thereafter cooled and subjected to countercurrent Washing with a paraillnic solvent having a boiling range different from that of the desired product and also from the higher boiling selective solvent. This washing operation is regulated so that practically all .of the non-aromatic hydrocarbons initially present in the extract phase are washed out along with a very small amount of aromatica The resulting `extract phase is then distilled to separate the desired components, such as the toluene, from the wash g5 solvent, the anti-solvent and the high boiling sefor the most part, olens having boiling points in the range of 220 F.250 F. and parafilns having boiling points generally higher than that of toluene. The oleiins may be removed by acidtreating with associated relatively high losses' of toluene. Total removal of parans can be accom- I Vplished only by an extremely effective distillation operation using equipment not generally available for commercial use. A portion of the toluene associated with the paraffin cuts may be recovered by recycling.

It the vapor phase extraction process isr'soperated totake overhead only paramns and the resulting hydrocarbons remaining in the extract phase are then stripped of solvent and subjected to a second vapor phase extraction, little improvement in purity of the aromatic phase is obtained. 'l'his phenomenon is due to the vfact that the higher boiling parailins and the olens have approximately the same vapor pressure in the presence of the selective solvent as does the toluene. By subjecting the hydrocarbon material to alternate vapor phase extraction and distillation with recycling oi the intermediate products, it would be possible to obtain substantially all of the tolulective solvent.

The main object of my present invention, therefore, is to provide selective solvent means for recovering from a mixture of hydrocarbons, a desired component in high yield and possessing a high degree of purity.

A more specific object of my present invention is tosolvent extract a mixture ofkhydrocarbons to secure a desired component in high yields and of a high degree of purity, in a manner eiecting Other and further objects of my present invention will appear from the following more detailed description and claims.

The accompanying drawing shows diagrammatically an arrangement of apparatus elements in which a preferred modification of my invention may be carried into practical effect. I shall now set forth a specific example describing a preferred modification of my invention and'in so doing I shall referto the accompanying drawa.v steam-cracked `naphtha fraction containing toluene, is charged into the system thru line l and thence discharged into a fired coil 3 disposed in a furnace 5 where the fraction is heated to vaporize the charging oil and thence withshown.

drawn thru line 6 and discharged into a primary 1fractionating column I0. From fractionatlng column I a low boiling fraction is withdrawn thru line` l2 and a high boilingfraction is withdrawn thru line` I5. These fractions arel re jected from the present system. A middle fraction boiling within the range of from 180 F. to-V 260 F. is withdrawn thru line 20 and heated in a iired coil 22 disposed in a furnace 24 to a temperature of approximately 220 F. to substantial vaporization, and thence discharged into extraction column 30 where it is treated with a solvent, such as phenol discharged from line 35 into tower 30; A rainate phase is recovered from column 30 thru line 31. This raiiinate .phase contains substantially no aromatics but consists essentially of paralns and oleilns plus a small amount of solvent, and is processed to recover the, solvent which is returned-to the system in equipment not .An extract phase is withdrawn from column 30 thru line 40 where it may be admixed with an anti-solvent, such as water, up to of the volume of phenol. This anti-solvent -is added thru line 38 and is addedfor the purpose of reducing the solubility of non-aromatics in the phenol. Thence -the mixture Yis discharged into a cooler 44 where it is cooled to a temperature of d '60 F.120 F. and thence discharged thru line 42 into a wash tower 48where it is washed with 30 liquid pentane fed into said tower thru line i0. An overhead fraction, comprising the liquid pentane with a small amount of solvent, non-aromatichydrocarbons and minor amounts of toluene from tower 48, is withdrawn overhead thru line 52 and charged to a furnace 56 where it is heated to partial vaporization (around 400 F.- 600 FJ, then withdrawn thru line 58 and discharged into a fractionating column 60 from from me bottom or aan an thru une llo and recycled to line and thence into extraction tower 30.

vention is applicable to any feed stock containing Pressure 1 toluene. Other aromatics may be recovered in a similar manner from suitable feed stocks. Furthermore, my invention includes the recovery of other hydrocarbons from mixtures thereof, such as the. recovery of butadiene, from a C4 hydrocarbon mixture. In the example given, phenol is the aromatic selective solvent and H2O is employed`as the anti-solvent. Other selective solvents include furfural, cresylic acid, etc. Other anti-solvents include low molecular weight aliphatic alcohols including polyhydric alcohols.

Good results are obtained in recovering toluene from hydrocarbon oils by operating in the following range of conditions in the extraction zone:

Proportion of phenoL-.. 100 to 300 volume per cent of feed Temperature in extraction tower Feed inlet-220 F.

Tower top-210 F. Tower bottom-320 F. Atmospheric In the wash tower 5-15 vol. per cent of H2O based on the phenol is employed.

The amount of wash solvent is 50 to 200 volume which three overhead fractions are recovered as Per cent 0f the Volume 0f extract- The temperafollows: rst, a wash solvent fraction which is withdrawn thru'line 62, cooled in a cooler 81, and returned thru lines 68 and 50 to wash tower 48;

a vside stream fraction consisting of the antisolvent which is withdrawn thru line 58 and is returned by means' not shown to line 39 and hence to tower 30; a. side stream fraction consisting of non-aromatic together with a small amount of aromatic hydrocarbons is withdrawn thru 1in.63; this fraction is normally rejected from the system but may be recycled to line l for further treatment; and a bottoms fraction which is withdrawn thru line 10, the said bottoms wash/tower 48 thru line 80. thence heated in a coil 82 disposed in a furnace 85, thence withdrawn thru line 88 and discharged into a fractionating column 90 from which wash solvent is recovered thru line 00 and recycled thru lines 68 and 50 to wash tower 48. A side stream comprising the anti-solvent is withdrawn thru line 02 and recycled to line 39 for further use in the wash column 48. Toluene is recovered as a side stream thru line 104. The solvent is recovered ture in this tower may be from 70 F. to 100 F.

I claim:

1. The method of recovering desired aromatic hydrocarbon components from a. naphtha containing said aromatic components and non-aromatic components which comprises vaporizing said naphtha, fractionating the vapors, recovering a naphtha fraction containing said desired aromatic components and having a boiling range spreading over. up to about F., contacting said fraction substantially vaporized with about to 300% by volume of a liquid selective solvent for the desired aromatic components at temperatures ranging from about 210 F. to about 320 F. to produce an extract phase containing said desired aromatic components together with about`5% to 10% of non-.aromatic components and a vaporous raffinate, separating said extract phase from said vaporous raffinate, adding about 5% to 15% by volume based on the amount of selective solvent of an antisolvent to said extract phase, contacting said extract phase with about 50% to 200% by volume of a'parainic wash solvent for said non-aromatic components in a. washing zone at a. temperature of about 70 to 100 F. to wash out of said extract phase practically all of said non-aromatic components together with a minor amount of the desired aromatic components, said wash solvent having a boiling range different from that of said desired aromatic components, withdrawing said extract phase kfrom said washing zone and recovering said desired aromatic components from said exess water is added to the extract phase recovered from the extraction zone prior to the washing step.

3. The method set forth in claim 1 in which the wash solvent is pentane.

4. The method of recovering toluene from a naphtha containingtoluene and non-aromatic components which comprises obtaining a naphtha fraction boiling within therange of from about 180 F. to about 260 F., vaporizing said fraction, contacting said vaporied fraction with about 100% to 300% by volume of a liquid selective solvent for toluene at a temperature ranging from about 210 F. to about 320 F. under such conditions as produce a liquid extract phase containing toluene together with about 5% to 10% non-aromatic components and a vaporous railnate, separating said extract phase from said vaporous raillnate, adding an antisolvent to said extract phase, contacting said extract phase nic wash solvent in a washing one at a temperature of about '70 F. to 100 F.. in such a manner that practically all of the non-aromatic components together with a minor amount of toluene are washed out of said extract phase, said wash solvent having a boiling range different from thaty of toluene, withdrawing said extract phase from said washing zone and recovering toluene therefrom by distillation.

5. The method set forth in claim 4 in which the selective solvent is phenol in liquid form.

6. The method set forth in claim 4 in which the selective solvent is liquid phenol and in which process water is added to the phenol withdrawn from the extraction zone which water serves as an anti-solvent, and thereafter the mixture of anti-solvent and phenol extract is discharged with about 50% to 200% by volume of a parafinto the Washing zone.

7. The method set 101th in claim 4 in which the wash solvent is permane.

CHESTER L. READ. 

